Extraction articles and methods

ABSTRACT

This invention provides a one-piece multilayer article for use in solid phase extraction that includes at least two porous support layers and a solid phase extraction medium, wherein the porous support layers are thermo-mechanically attached at at least one thermo-mechanical attachment site. At least one of the porous support layers can be a prefilter layer.

This application is a 371 of PCT/US99/21113 filed on Sep. 13, 1999,which claims benefit of U.S. provisional application 60/100,242 filed onSep. 14, 1998.

FIELD OF THE INVENTION

This invention relates to extraction articles, particularly to aone-piece multilayer article for use in solid phase extraction inisolation, separation, and analysis techniques. The invention alsorelates to methods of separation and analysis using the articles, aswell as to methods of making the one-piece multilayer article.

BACKGROUND OF THE INVENTION

Generally, the art of separation science, which involves extraction andchromatography, has two main objectives. One is high yield extractionand recovery of a targeted analyte and the other is a rapid rate ofextraction and elution. A specific type of extraction used forseparation is solid phase extraction, also known as SPE. SPE is a methodof sample preparation that removes and concentrates an analyte from aliquid sample by absorption or adsorption onto a disposable solid phasemedium. This is followed by elution of the analyte with a solventappropriate for analysis. In SPE two devices commercialized to balancethe two competing objectives described above are cartridges (such asthose available under the trade designation BAKERBOND SPEEDISK from J.T. Baker, Phillipsburg, N.J.) and disks (such as those available underthe trade designation DFP disks from Whatman, inc., Clifton, N.J.).

Solid phase extraction cartridges typically consist of a column of loosesorbent material as the extraction medium. This sorbent material has asufficient surface area to reduce the problems of sample processingusing gravity or vacuum. This design has certain inherent disadvantages.For example, such cartridges may typically have a small cross-sectionalarea of extraction media, which results in slow processing, as well aschanneling, which reduces analyte retention. Solid phase extractiondisks eliminate these disadvantages.

Commercial solid phase extraction disks include particle loadedmembranes of various diameters as the extraction medium. For example,one such disk comprises a membrane that includes sorbent particles(e.g., C8- and C18-bonded silica particles) immobilized in a web ofpoly(tetrafluoroethylene) (PTFE) microfibrils. Another such diskincludes a web of glass microfibers impregnated with chemically bondedsilica sorbents such as C18 aliphatics. For general use, SPE disks canbe supported on a glass or polymer frit disk in a standard filtrationapparatus, using vacuum to generate the desired flow of sample throughthe disk.

Most commercial SPE products are designed to be used with a separateprefilter if the sample of interest (e.g., wastewater) contains asignificant amount of solid material (e.g., suspended solids) that couldplug the SPE medium. Commercial prefilters are typically constructed ofnatural fibers such as celluloses. glass fibers, or syntheticthermoplastic fibers such as polypropylene, polyester, andpolyethyleneterephthalate. Typically, these prefilters are designed toprevent the SPE medium from becoming plugged. The prefilters aretypically supplied separately from the SPE products.

SPE products are still needed that are capable of achieving highrecoveries of analytes from a liquid sample while maintaining highsample flow-rates with little or no plugging of the disk during use. Thelatter problem can hinder effective analysis. This is particularly truefor the extraction of nonpolar hydrocarbon extractable analytes fromwater. Ease of use and simplicity in procedure are also importantconsiderations for the end user. Other factors the user may consider inchoosing extraction media include the capability of being used with avariety of equipment and glassware including automatic analysisapparatus. The present invention provides an extraction disk that hasone or more of these characteristics.

SUMMARY OF THE INVENTION

This invention provides a one-piece multilayer article for use inextraction, isolation, separation, and analysis techniques. In oneaspect, the invention provides an article that includes a first poroussupport layer thermo-mechanically attached to a second porous supportlayer (preferably, welded together) at at least one attachment site, andtherebetween, a solid phase extraction medium comprising a fluoropolymer(preferably, in the form of a membrane) is disposed. Preferably, atleast one of the porous support layers is made from thermoplasticmaterial.

Although the extraction articles specifically described herein includethree layers, more than three layers can be incorporated into thearticles if desired as long as at least one each of the three layers(first porous support layer, second porous support layer, and SPEmedium) described herein are present. The multilayer articlesspecifically described herein may come in a variety of shapes and formsincluding circular disks, squares, ovals, etc.

The fluoropolymer solid phase extraction (SPE) medium can be in avariety of forms, such as fibers, particulate material, a membrane,other porous material having a high surface area, or combinationsthereof. Preferably, the SPE medium is in the form of a membrane thatincludes a fibril matrix and sorptive particles enmeshed therein. Thefibril matrix is typically an open-structured entangled mass ofmicrofibers. The sorptive particles typically form the active material.By “active” it is meant that the material is capable of capturing ananalyte of interest and holding it either by adsorption or absorption.The fibril matrix itself may also form the active material, althoughtypically it does not. Furthermore, the fibril matrix may also includeinactive particles such as glass beads or other materials for enhancedflow rates.

The porous support layers can be made of a wide variety of porousmaterials that do not substantially hinder flow of the liquid of thesample of interest. Typically these materials are those that are capableof protecting the solid phase extraction medium from abrasion and wearduring handling and use. The material should be sufficiently porous toallow the liquid sample to flow through it, and preferably, able toretain particles contained within the SPE medium. Preferably, thesupport layers are made of a nonwoven material. It is also preferredthat both the first and second porous support layers are very similar incomposition (as opposed to structure), and more preferably, they are thesame.

In a preferred embodiment, one of the porous support layers is aprefilter layer, preferably made of a nonwoven material. (For ease ofdescription, as used herein the first porous support layer will bedesignated as the preferred porous support layer that is a prefilter;however, either the first or second porous support layer can be aprefilter). More preferably, the first porous support layer is anonwoven web of blown microfibers, most preferably melt blownmicrofibers. Such “melt blown microfibers” or “BMF” are discrete, fine,fibers prepared by extruding fluid, fiber-forming material through fineorifices in a die, directing the extruded material into a high-velocitygaseous stream to attenuate it, and then solidifying and collecting themass of fibers. In preferred embodiments, the prefilter layer includes anonwoven web of melt blown polyolefin fibers, particularly polypropylenefibers.

In embodiments where one of the porous support layers is a prefilter, itis preferred that the prefilter have the following characteristics: asolidity of no greater than about 20%; a thickness of at least about 0.5millimeters (mm); and a basis weight of at least about 70 grams persquare meter (g/m²). As used herein, solidity refers to the amount ofsolid material in a given volume and is calculated by using therelationship between weight and thickness measurements of webs. That is,solidity equals the mass of a web divided by the polymer density dividedby the volume of the web and is reported as a percentage of the volume.The thickness refers to the dimension of the prefilter through which thesample of interest flows and is reported in mm. The basis weight refersto mass of the material per unit area and is reported in g/m².

The one-piece multilayer extraction disks can be used in a wide varietyof solid phase extraction processes to remove a broad spectrum ofanalytes from a wide variety of liquid samples (optionally containingparticulate material). Preferably, both the solid phase extractionmedium and the prefilter are chosen to remove the analyte of interest.That is, in certain preferred extraction procedures a prefilter ischosen such that it helps capture the targeted analyte, therebyincreasing the recovery yield. In certain preferred embodiments, thearticle of the invention is designed to remove hydrocarbon extractables(e.g., nonpolar hydrocarbons such as oil and grease) from a liquidsample (e.g., water). One such embodiment includes a prefilter layer, apolytetrafluoroethylene (PTFE such as TEFLON) fibril matrix containingboth C18 bonded silica particles and glass beads, and a support layer.The prefilter is a polyolefin (e.g., polypropylene or polyethylene)blown microfiber web, which can act both as a depth filter and as amedium to help capture the hydrocarbon extractables. This combination ofa prefilter with the PTFE fibril matrix and C18 bonded silica particlesresults in high efficiency extractions. Although this prefilter designis not limited to hydrocarbon analysis, a synergistic effect resultsfrom the use of a prefilter that is capable of sorbing nonpolarhydrocarbon materials from water along with a C18 PTFE membrane. Inother applications the action of the prefilter may only reside in itsability to function as a filter for suspended solids, for example, andnot as an adjunct to the sorption capabilities of the solid phaseextraction medium.

The present invention also provides methods of extracting an analytefrom a sample using the one-piece multilayer solid phase extractionarticle as well as methods of preparing the article.

The method of making a one-piece multilayer extraction article of thepresent invention involves thermo-mechanically attaching the firstporous support layer to the second porous support layer. In a preferredembodiment an ultrasonic welder is used to form the thermo-mechanicalattachment site between the two support layers. Bound within thethermo-mechanical attachment site is the SPE medium. Preferably, theprocess of welding substantially simultaneously attaches the poroussupport layers together while capturing the SPE medium and cuts thearticle into a shape and dimension.

In a preferred embodiment, the present invention provides a method ofultrasonically welding a one-piece multilayer extraction article thatcomprises the steps of: a) stacking a first porous support layer, asecond porous support layer, and a layer of solid phase extractionmedium comprising a fluoropolymer therebetween, b) positioning the stackof layers in an ultrasonic welder that comprises an anvil and anultrasonic horn; and c) pinching the stack of layers between the anviland the horn to form a thermo-mechanical attachment site between thefirst and second porous support layers, and the solid phase extractionmedium is bound within the thermo-mechanical attachment site.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a cross-section of a one-piece multilayer extraction articleof the present invention.

FIG. 2 is a cross-sectional view of a portion of an ultrasonic weldingapparatus for making a one-piece multilayer extraction article, beforewelding.

FIG. 3 is cross-sectional view of a portion of an ultrasonic weldingapparatus for making a one-piece multilayer extraction article, duringwelding.

FIG. 4 is an exploded view of section A of FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIG. 1, the present invention provides a one-piecemultilayer extraction article 10 that includes a first porous supportlayer 12 and a second porous support layer 14 thermo-mechanicallyattached at at least one attachment site, having a layer of a solidphase extraction medium 18 therebetween. The solid phase extractionmedium comprises a fluoropolymer, and at least one of first poroussupport layer 12 and second porous support layer 14 is a thermoplasticmaterial. Both first porous support layer 12 and second porous supportlayer 14 are in intimate contact with SPE medium 18. Preferably, thethermo-mechanical attachment site is located at the perimeter 16 ofarticle 10. The solid phase extraction medium 18 preferably includes afibril matrix 20 and sorptive particles 22 enmeshed therein. Optionally,but preferably, the fibril matrix 20 may also include inactive (i.e.,nonsorptive) particles such as glass beads. The fibril matrix 20 is anopen-structured entangled mass of microfibers. The sorptive particles 22are capable of taking up an analyte of interest and holding it either byadsorption or absorption.

First porous support layer 12 can be made of a wide variety of porousmaterials. It is preferably a nonwoven web, and more preferably, a blownmicrofiber web. Preferably, the blown microfiber web includes polyolefinfibers, and more preferably polypropylene fibers, although otherpolymers can be used if desired.

In a preferred embodiment, the first porous support layer is a prefilterthat removes particulate material, such as suspended solids, from asample of interest, such as wastewater. The prefilter preferably reducesclogging of the solid phase extraction medium, which would otherwiseincrease extraction times. Preferably, and significantly, in certainembodiments, the prefilter also aids in capturing the analyte ofinterest, such as nonpolar hydrocarbon extractables, which enhancessorption capacity of the one-piece multilayer extraction disk. In thisarrangement, the prefilter and the inner solid phase extraction mediumare made of materials that have similar sorption characteristics for theanalyte of interest. Alternatively, the prefilter can be used to capturecontaminants that can interfere with the analysis of the desiredanalyte, which is collected by the inner solid phase extraction medium.In this arrangement, the prefilter and the inner solid phase extractionmedium are made of materials that have differing sorptioncharacteristics for the analyte of interest.

The second porous support layer 14 assists in supporting and reducingabrasion to the inner solid phase extraction medium while the disk is inuse and during handling. The support layer 14 can include a wide varietyof porous materials. Typically it is a nonwoven web, and preferably amicrofiber web, more preferably a melt blown microfiber web. For moreeffective bonding by ultrasonic welding, it is preferred that thematerial of the first and second porous support layers include similartypes of polymeric material. Preferably the support layers are the samepolymeric material.

In a preferred embodiment of the invention, the two porous supportlayers 12 and layer 14 are sonically welded together to encase a solidphase extraction medium in between and form a one-piece integral unit.The two (or more) outer layers may alternatively be bonded togetherusing a hot press. Preferably, either method can be used to cut and meltthe edges together to form a single unit.

For preferred embodiments, the capability of creating an attachment siteincorporating a low surface energy layer (e.g., PTFE) with highersurface energy thermoplastic layers (e.g., polypropylene) wasunexpected. The presence of the low surface energy material was thoughtto prevent or inhibit effective bonding between the two (or more) outerlayers.

Porous Support Layers

The one-piece multilayer SPE article of the invention comprises a firstand second porous support layer. Optionally, one of the support layerscan be a scrim, i.e. a thin porous support layer. As a scrim, thesupport layer provides support for the SPE medium and helps protect theSPE medium from potentially damaging abrasion during shipping andhandling. This support and protection is achieved by intimatelycontacting the porous support layers with the SPE medium and bythermo-mechanically attaching the first and second support layers withthe SPE medium disposed therebetween. Preferably, the thermo-mechanicalattachment is located at an edge in the article. In a preferredembodiment where the article is in the form of a circular disk, thethermo-mechanical attachment is located at the perimeter of the disk,more preferably, around the total circumference of the disk. Preferably,at least a portion of the SPE medium is pinched or wedged between thetwo porous support layers to reduce distortion of the SPE medium whilebeing handled.

The porous support layers may consist of any suitable material that doesnot unduly restrict the flow of water or other sample liquid through theweb or in any way reduce the function of the SPE medium. The materialfor the two porous support layers should be chosen such that they arecapable of being thermo-mechanically attached. Preferably, at least oneof the porous support layers is a thermoplastic polymeric material. Morepreferably, both the first and second porous support layers comprise asimilar type of thermoplastic polymeric material, and most preferably,the layers are the same thermoplastic polymeric material. Suitablethermoplastic polymeric materials include polycarbonates, polyesters,polyamides, and polyolefins such as polyethylene, polypropylene,ethylene/propylene copolymers, and blends thereof. Copolymers as usedherein include random, block, grafted, etc. polymers prepared from twoor more different types of monomers.

The thermoplastic polymeric material is preferably provided in the formof a fibrous web. Such fibrous material can be made of either spunbonded or spun laid fibers, blown microfibers, or the like. A melt blownmicrofiber (BMF) web is more preferred.

Preferably, at least one of the porous support layers is made ofpolypropylene with a basis weight of about 14 grams per square meter(g/m²) to about 70 g/m², and more preferably, about 17 g/m² to about34.0 g/m². The thickness is typically less than about 1 mm.

The porous support layers can be embossed if desired for enhancedstrength. For example, heat embossing at points approximately 0.006 cm²area spaced approximately 1.25 mm on center can be instituted. Theporous support layers should have sufficient porosity to allowunrestricted flow. Materials suitable for the support layers that arecommercially available include a nonwoven web available from BBANonwovens of Simpsonville, S.C. under the product name CELESTRA.

In a preferred embodiment, one of the porous support layers is aprefilter. There are two basic types of mechanical filtrationmechanisms—surface and depth filtration. Filtration occurs when theporosity of a filter medium allows the carrier fluid to pass through thepores of the medium itself while larger particles (dirt or suspendedsolids) are retained on the upstream surface of the filter medium. Ifthe particles fail to pass through the tortuous path of the filtermedium it then becomes lodged in the filter reducing the overallporosity for fluid flow.

Surface filtration works by direct interception of the particlesreducing the effective pore size of the filter. A cake or layer of theparticles builds on the surface, forming a filtration medium havingincreasingly smaller pore size until fluid flow eventually stops and thefilter is considered plugged.

Depth filtration occurs when a significant amount of thickness or voidvolume (or dirt holding capacity) is provided by the filter medium suchthat a longer and more random path for fluid flow occurs. This createsmore possibility for retention of particles as well as directinterception of these particles within the thickness of the filtermaterial. A depth filter is more effective in reducing plugging becausethere is more depth loading of the particles (dirt) rather than surfaceinterception and subsequent cake development. The carrier liquid isstill able to find a path through the filtration medium. In a depthfilter, generally, larger particles tend to become trapped first whilethe smaller particles pass deeper into the pores of the filter mediumbefore lodging therein.

The prefilter support layer of the present invention can function as adepth filter. This makes them particularly suitable for evaluatingenvironmental waters or biological samples containing suspended solidshaving widely distributed particle sizes.

To enhance the function of the prefilter support layer as a depthfilter, various characteristics are balanced to avoid plugging andenhance filtration. These characteristics include solidity, thickness,basis weight, internal pore volume, fiber diameter, etc.

For example, smaller fiber diameter provides a larger surface area thatis available for oil extraction. However, smaller diameter fibers formless dense webs and fibers can be more fragile. Larger diameter fibersprovide greater strength and better shape retention. Preferably, thefibers of the prefilter support layer have a diameter of at least about0.1 microns, more preferably 1.0 microns, and most preferably 7 microns.Preferably, the fiber diameter is no greater than about 20 microns, morepreferably 15 microns, and most preferably 12 microns.

Preferably, the prefilter support layer has a solidity of no greaterthan about 20%, more preferably, no greater than about 15%, and mostpreferably, no greater than about 10%. Preferably, the solidity is atleast about 5%. Preferably, the prefilter has a thickness of at leastabout 0.5 mm, more preferably, at least about 1 nm. and most preferably,at least about 2 mm. Preferably, the thickness is no greater than about0.5 mm. Preferably, the prefilter has a basis weight of at least about70 g/m², more preferably, at least about 100 g/m², and most preferably,at least about 200 g/m². Preferably, the basis weight is no greater thanabout 300 g/m².

These parameters contribute to the void volume of the prefilter. Forexample, a thickness of at least about 0.5 mm to maintain a highinternal void volume. A high internal void volume allows for a largesurface area and tortuous paths for the analyte to travel with little orno pressure drop.

A wide variety of fibrous materials can be used to make the prefiltersupport layer of the present invention. The choice of material used inmaking the prefilter can be matched, for example, by polarity, to theanalyte being extracted if it is desired to enhance extraction.Alternatively, it can be matched to contaminants that can detrimentallyaffect the quantitative or qualitative evaluation of the analyte ofinterest. For example, for enhancing the separation and analysis ofhexane extractables such as oil and grease, polyolefins such aspolypropylene, polyethylene, polybutylene, halogenated derivativesthereof, and blends or copolymers thereof are suitable. Polypropylene isa particularly preferred material because it is easily processed. Othersuitable materials include polycarbonates, polyesters, polystyrene,polyamide, and the like. Blends or copolymers of various materials canalso be used.

The prefilter support layer can be made of spun bonded fibers, cardedfibers, spun laid or spun laced fibers, blown microfibers, or the like.A blown microfiber (BMF) web is preferred. For making a BMF web, a resinhaving a melt flow index of about 43 to about 400 is particularlypreferred. Commercially available examples of resins can be obtainedfrom Fina Petroleum of Houston, Tex. A preferred polypropylene resin isavailable under the trade designation FINA 3860.

Microfiber webs are generally formed by melt blowing techniques such asdescribed in Wente, Van A. Super Fine Thermoplastic Fibers, IndustrialEngineering Chemistry, 342, Volume 48. page 1342 et seq (1956), as wellas U.S. Pat. No. 2,464,301 (Francis), U.S. Pat. No. 2,612,679 (Ladisch),and U.S. Pat. No. 3,073,735 (Till et al.). Furthermore, specificexamples of materials useful as prefilter layers include those describedin U.S. Pat. No. 3,764,527 (Sohl), U.S. Pat. No. 4,052,306 (Schwartz etal.). and U.S. Pat. No. 4,103,058 (Humlicek). Briefly, a resin is heatedabove its melt temperature in either a single or twin screw extruder andfed through a die under high pressure. Fibers are formed at the exit ofthe die and blown onto a collector at such a speed as to produce acontinuous web at a desired basis weight.

The basis weight of the web varies depending the rate at which thecollector is moved through the gaseous stream. Examples of commerciallyavailable materials suitable for the prefilter support layer of theinvention includes an oil sorbent polypropylene BMF web, available from3M Co. of St. Paul, Minn. under the product designation OILSORB T-151BMF.

Optionally, either the first or second porous support layers, or both,can comprise multiple layers of porous material, as long as at least oneof the multiple layers of porous material is in intimate contact withthe SPE medium.

Solid Phase Extraction Medium

The solid phase extraction medium can include a wide variety ofmaterials in various forms. For example, it can be in the form ofparticles, which may be loose or immobilized, fibers, a membrane, orother porous material that have a high surface area. In a preferredembodiment, the SPE medium is a fibril matrix having sorbent particlesenmeshed therein. Such sorbent particles are the “active” element of themedium in that they capture the analyte of interest.

The fibril matrix can include any of a wide variety of fibers. Suitablefibers include glass fibers, polyolefin fibers, particularlypolypropylene and polyethylene microfibers, aramid fibers,polytetrafluoroethylene fibers, and natural cellulosic fibers. Mixturesof fibers can be used, which themselves may be active or inactive. Thematrix forms a web that is preferably about 15 mm to about 40 mm thick.

The sorbent (active) particles are typically insoluble in an aqueous ororganic liquid. They can be made of one material or a combination ofmaterials as in a coated particle. They can be swellable ornonswellable, although they are preferably nonswellable in water andorganic liquids. They are chosen for their affinity for the targetanalyte. Water swellable particles are described in U.S. Pat. No.4,565,663 (Errede et al.); U.S. Pat. No. 4,460,642 (Errede et al.); andU.S. Pat. No. 4,373,519 (Errede et al.). Particles that are nonswellablein water are described in U.S. Pat. No. 4,810,381 (Hagen et al.); U.S.Pat. No. 4,906,378 Hagen et al; U.S. Pat. No. 4,971,736 (Hagen et al.);and U.S. Pat. No. 5,279,742 (Markell et al.). Mixtures of sorbent(active) particles can also be used.

In a preferred embodiment, coated particles can be enmeshed in the SPEmedium. The base particles can include inorganic oxides such as silica,alumina, titania, zirconia, etc., to which are covalently bonded organicgroups. For analysis of nonpolar hydrocarbon (e.g.,hexane) extractablecompounds, for example, covalently bonded organic groups such asaliphatic groups of varying chain length (C2, C4, C8, or C18 groups) canbe used. Preferred C18 bonded silica particles are available from VarianSample Preparation Products, Harbor City, Calif.

Optionally, inactive particles or other materials or mixtures thereof,can be used in the solid phase extraction medium. Such materialsinclude, for example, glass spheres and silica particles. Solid glassspheres are particularly preferred because they have high compressivestrength and surface hardness. Thus, the solid phase extraction mediumhas a higher compressive strength and surface hardness when solid glassspheres are enmeshed within the fibril matrix. Solid glass spheres alsoallow for better stress distribution and liquid flow characteristics tothe media when subjected to vacuum or pressure drop during extractionand elution. Suitable solid glass spheres can be obtained from PottersIndustries Inc. of Parsippany, N.J. under the product name SPHERIGLASSor from 3M Co. (St Paul. Minn.) under the product name TUNGO Beads. Theypreferably range from about 52 microns (micrometers or μm) to 105microns in particle size (i.e., the largest dimension, which istypically, the diameter), and have a mean volume particle size of about70 microns. The particle size is determined by light scatteringmethodology.

Preferred embodiments of the SPE medium of the one-piece multilayerextraction disks of the present invention include both active andinactive particles. The active particles are preferably present in theSPE medium in an amount of about 3 weight percent (wt-%) to about 10wt-%, based on the total weight of particles. The inactive particles arepreferably present in the SPE medium in an amount of about 90 wt-% toabout 97 wt-%, based on the total weight of the particles.

Examples of suitable SPE media are described in U.S. Pat. No. 5,279,742(Markell et al.), U.S. Pat. No. 4,906,378 (Hagen et al.), U.S. Pat. No.4,153,661 (Ree et al.), U.S. Pat. No. 5,071,610 (Hagen et al.), U.S.Pat. No. 5,147,539 (Hagen et al.), U.S. Pat. No. 5,207,915 (Hagen etal.), and U.S. Pat. No. 5,238,621 (Hagen et al.). A particularlypreferred SPE medium consists of C18 bonded silica beads (approximately5-6 wt-%, based on the total weight of the beads), which sorbhydrocarbon compounds from water, and glass beads having a mean volumeparticle size of about 70 microns (approximately 94-95 wt-%, based onthe total weight of the beads), which aid in rapid flow-rates, enmeshedwithin PTFE (approximately 1-2 wt-%, based on the total weight of theSPE medium).

The PTFE matrix can be prepared according to the procedure described inU.S. Pat. No. 4,906,378 (Hagen et al.). Briefly, this involves the stepsof blending the particulate material with a polytetrafluoroethyleneaqueous dispersion in the presence of sufficient lubricant water toexceed the absorptive capacity of the solids, yet maintain a putty-likeconsistency, subjecting the putty-like mass to intensive mixing at atemperature of about 50° C. to about 100° C. to cause initialfibrillation of the polytetrafluoroethylene particles, biaxiallycalendering the putty-like mass to cause additional fibrillation of thepolytetrafluoroethylene particles while maintaining the same watercontent and drying the resultant sheet.

Optionally, the SPE layer can include multiple layers suitable material.In such cases, preferably, a third porous support layer is disposedbetween layers of SPE medium.

Other SPE products that can be used in the present invention. Suchproducts are available from Whatman, Inc. of Clifton, N.J., CPIInternational of Santa Rosa, Calif., and J. T. Baker, Phillipsburg, N.J.These products typically include silica particles with coatings ofcovalently bonded aliphatic hydrocarbons. For some of the products, theparticles are enmeshed within glass fibers. The latter products may beprotected by an outer scrim, which may or may not be used in theconstructions of the present invention.

Method of Making a One-Piece Disk Construction

The one-piece multilayer SPE article can be made using a variety oftechniques. In one aspect, the outer edges of the two outermost layers,i.e., first and second porous support layers, are thermo-mechanicallyattached at their edges. This is a particularly difficult procedure,however, when the inner SPE medium includes a PTFE matrix enmeshed withparticulate material. Thus, for preferred embodiments of the presentinvention, a method of construction involves ultrasonically welding thetwo porous support layers. Preferably, at least a portion of the SPEmedium is bound within the attachment site. In this case, the SPE mediumcan be physically encased or wedged in the weld. Preferably, thethermo-mechanical attachment is formed by ultrasonically welding thesupport layers and substantially simultaneously cutting the layers intoa desired shape and dimension.

Due to the low surface energy of PTFE, it typically resists molten resinflow and therefore has minimal capability for being bonded. Thisresistance thus prevents the formation of any permanent weld seam.However, by taking advantage of the different material characteristicsbetween the multiple layers, it has been surprisingly found thatultrasonic energy can be applied under pressure through the PTFE layerbetween an anvil and a horn, thereby removing the barrier responsiblefor preventing the formation of the weld seam. Furthermore, since theweld seam is highly localized it is possible to encase the PTFE membranebetween the two outermost layers without damaging or crushing theinternal web, over the usable internal diameter. The result is aone-piece multilayer extraction disk capable of providing goodextraction and flow rate performance.

Referring to FIG. 2, in a preferred embodiment, a web or membrane of SPEmedium 18, which preferably includes a PTFE matrix 20 loaded with C18coated particles, is positioned between two porous support layers 12 and14. Optionally, the PTFE matrix 20 may also include inactive (i.e.,nonsorptive) particles such as glass beads. Preferably, porous supportlayers 12 and 14 are made of a polyolefin material. Webs 12, 14, and 18are positioned over a cut-and-seal ultrasonic welding anvil 30 of anultrasonic welder (e.g., Branson 900 series Ultrasonic Welder availablefrom Branson Ultrasonics, Inc. of Danbury Conn.). The air pressure ofthe welder are typically set at about 50 pounds per square inch (psi) toabout 100 psi, preferably about 68 psi to about 70 psi.

The welding anvil 30 converts the layers into a one-piece multilayerformat, by a combination and substantially simultaneous plunging andwelding operation. This process provides a thermo-mechanical attachmentsite between the two porous support layers 12 and 14. During the plungewelding operation, a flat, hardened steel ultrasonic horn 32 traverses,firmly pressing the three layers 12, 14, and 18 against a weldingsurface 34 located on anvil 30. Anvil 30 also has a cutting angle α ofno less than about 20°, preferably about 25°. Cutting angle α may not begreater than about 40°, preferably, not greater than about 35°. Weldingsurface 34 measures no less than about 0.01 centimeter (cm), preferably,no less than about 0.02 cm wide. Additionally, welding surface 34 is nogreater than about 0.04 cm, preferably, no greater than about 0.03 cmwide.

Referring to FIG. 3, it is shown that the layers 12, 14 and 18 arecompressed during a pinching and welding operation. During the pinchingoperation, ultrasonic energy is applied under pressure. The weld timemay be set at a low setting of about 0.5 second, preferably, about 0.9second. A high setting for the weld time may be 1.5 seconds, preferably,about 1.0 second. The ultrasonic energy from the welder then melts andbonds the two outer nonwoven webs 12 and 14 together such that themolten material forms a localized weld seam 36 about the perimeter ofthe article. See FIG. 4. A hold time may be set at about 0 second on thelow end, and preferably, about 0.15 second. On the upper end of the holdtime range, the hold time parameter for the welder may be about 0.25second, preferably, about 0.17 second. To complete the cutting action,the molten material along the outside circumference of the disk iscompressed causing the excess material 38 to flow away from the flat,thereby, resulting in a separation of the sealed article from thesurrounding laminate material.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention. All parts andpercentages are by weight unless otherwise indicated.

EXAMPLES Test Procedures

General Determination of Oil and Grease

Guidelines for determination of oil and grease and total petroleumhydrocarbons by extraction are outlined in EPA (Environmental ProtectionAgency) Method 1664 (“N-Hexane Extractable Material (HEM) and Silica GelTreated N-Hexane Extractable Material (SGT-HEM) by Extraction andGravimetry (Oil and Grease and Total Petroleum Hydrocarbons)”) aspublished by the EPA in April 1995.

SAE Fine Dust Flow Rate Determination Test

The impact of solids content of a sample on the flow rate of the samplealiquot through the SPE disk or SPE disk/pre-filter combination wascharacterized by challenging the SPE disk, the prefilter, and one-pieceSPE articles of the present invention with a known quantity of SAE FineDust suspended in water. Suspend solids samples containing 100, 150, and200±5 mg solids were prepared by suspending SAE (Society of AutomotiveEngineers) Fine dust (available from Powder Technology Inc., Burnsville,Minn. under the product name ISO12103-1, A2 Fine Test Dust) in one literof deionized water. Vacuum was applied to the extraction apparatus, theentire contents (one liter) of the challenge suspension introduced intothe extraction apparatus reservoir, and the flow time for the completepassage of water through the SPE disk, prefilter and one-piece SPEarticle for each challenge suspension was recorded.

General Procedures

Preparation of SPE Disk

A PTFE membrane comprising a polytetrafluoroethylene (PTFE) matrixhaving enmeshed therein C18 bonded silica particles (mean volumeparticle size=55 microns, supplied by Varian or United ChemicalTechnologies) and glass beads was prepared substantially as described inU.S. Pat. No. 4,906,378 (Hagen et. al.). The weight of the C 18 coatedbeads was 4-10 wt-% of the weight of the 70 micron glass beads (suppliedby 3M Company under the trade designation TUNGO). The C18 coatedparticles were added to the glass beads and a PTFE dispersion (suppliedby ICI Americas, Inc. under the trade designation FLURON, 1.5-4.0 wt-%based on the combined weight of the bead mixture) was added to thebeads. The resulting mixture was manually mixed to produce a dough whichwas placed on a heated two roll mill and repeatedly calandared toproduce a thin film comprising a PTFE matrix containing dispersed glassbeads (0.038-0.102 cm thick), which was subsequently cut into 47 and 90mm diameter disk formats.

The specific composition and properties of the SPE disks used in thepresent invention is shown in Table 1, although other variations of thecomponents can be made.

TABLE 1 Varian C18 6 wt % PTFE 2 wt % Thickness 0.064 cm Mill passes 8Durometer 35

Mill passes is the number of times the PTFE dough was passed between therollers of the two roll mill. Durometer, a hardness measurement,generally fell between 20 and 60.

Ultrasonic Welding Procedure

A Branson Ultrasonic Welder (Model 901AE, available from BransonUltrasonics, Danbury, Conn.) equipped with a cut-and-seal ultrasonicwelding anvil that was configured with a small 0.001 inch to 0.01 inchwide welding flat on its surface was used to prepare the one piecemulti-layer solid phase extraction articles of the present invention. Alayered construction comprising a SPE membrane positioned between twoporous thermoplastic polyolefin cover layers was threaded through alocating collar associated with the anvil, ultrasonic energy applied tothe horn, and the horn traversed toward the anvil, thereby pinching thelayered construction together. The middle SPE layer was captured in thebond line of the article as the outer polyolefin the layers were bondedtogether during the welding operation.

Method of Use of a One-Piece Multilayer Extraction Disk for Oil andGrease Extraction

Sample Pretreatment

The pH of the sample was adjusted to less than 2.0 with the addition of6N HCl or H₂SO₄. Suspended solids were allow to settle (overnight ifnecessary) and the liquid portion of the sample decanted from thesolids.

Manifold Setup

The filtration manifold was set up according to standard procedures,centering the extraction disk on the base of the filtration apparatusand clamping the reservoir in place on top of the disk using singlemanifold for 47mm disks (available from 3M Company, St. Paul, Minn.). Avacuum of 20-25 inches Hg (0.68-0.85 bar) was used for disk conditioningand analylate separations.

Disk Conditioning

The SPE disk and reservoir sides were washed with n-hexane(approximately 5-10 mL (sufficient solvent volume to cover the top ofthe disk) and the hexane drawn through the disk be application of vacuumto the collection flask. The disk was allowed to dry under vacuum forapproximately one minute, and then the vacuum was removed.

Methanol (10 ml) was added to the reservoir, vacuum applied to thecollection flask and a few drops of methanol drawn through the SPE disk,at which point the vacuum was removed, leaving enough methanol in thereservoir to cover the surface of the disk. The disk allowed to soak inthe methanol for 60 seconds to complete the conditioning.

Sample Extraction

The sample was poured or decanted into the reservoir and vacuum wasimmediately applied to the collection flask, drawing the sample throughthe SPE disk as quickly as possible. (If suspended solids were presentin the sample, care was taken to introduce as much of the liquidcomponent of the sample into the reservoir as possible beforeintroducing the solids component.) In the case where solids werepresent, the disk was not allowed to become dry before the solids wereadded. (Care was taken to insure maximum transfer of water from thesample container as possible.) After all the liquid had passed throughthe SPE disk, the vacuum was maintained for a maximum of 5 minutes todry the disk.

Sample Elution

The filtration assembly was equipped with a clean glass vial for eluatecollection. Hexane (10 mL) was added to the original sample containerand the closed container inverted several times to insure all the innersurfaces of the container were washed with hexane. The hexane wastransferred from the sample container to the disk using a disposableglass pipette, taking care to wash down the sides of the reservoirprior. A vacuum was carefully applied to the collection flask to pull afew drops of hexane through the disk and then the vacuum was removed.The disk was allowed to soak in hexane remaining in the reservoir for nomore than 2 minute, at which time it was slowly drawn through the SPEdisk by carefully applying a vacuum to the collection flask. The vacuumwas maintained for approximately 2 minutes after all the hexane hadpassed through the disk to dry the disk. The hexane extraction step wasrepeated a second time using another aliquot (10 mL) of hexane. Thesides of the glass reservoir were then washed with another aliquot (10mL) of hexane, the hexane drawn through the SPE disk by application of avacuum, and the disk dried by maintaining the vacuum for approximately 5minutes after all the hexane had passed through the disk.

The combined eluate and washes were then dried by filtering them overanhydrous sodium sulfate (5 g) maintained in a funnel. The sodiumsulfate and associated glassware were each subsequently rinsed withaliquots (5mL) to insure a quantative transfer of eluants.

Gravimetric Analysis

Standard gravimetric techniques were used to determine the oil andgrease content of the combined eluant and washes.

Example 1 and Comparative Examples C-1 and C-2

A SPE Disk assembly was prepared utilizing a SPE layer, prepared asdescribed above in “Preparation of SPE Disk,” a first porous supportlayer, Oilsorb™ T-151 BMF, available from 3M Co., St. Paul, Minn. and asecond porous support layer CELESTRA™ available from BBA Nonwovens,Simpsonville, S.C. The three layers were consolidated into a one pieceSPE disk (47 mm diameter) article using the ultrasonic welding proceduredescribed above, where the SPE Disk was disposed between the two blownmicrofiber webs. The article was tested substantially according to EPAMethod 1664 described above, except the 40 mg solution was replaced witha 10 mg suspension of a 50:50 hexadecane/stearic acid. The results,which are an average of seven samples, are presented in Table 2.

TABLE 2 Recovery Stdev. MDL ML 98% 0.216 0.679 2.159 10 mg/L spikes

The MDL is the Method Detection Limit. This is defined as the minimumconcentration of a substance that can be measured and reported with 99%confidence that the analyte concentration is greater than zero (takenfrom “Report of the Method 1664 Validation Studies”, EPA April 1995).The ML value is the level at which an entire analytical system producesa recognizable signal and an acceptable calibration point. It isdetermined by multiplying the MDL by 3.18 and rounding the resultingvalue to the number nearest 1, 2 or 5×10^(n), where n is an integer. Thevalue 3.18 is the ratio of the 10 times multiplier used in the ACS limitof quantitation calculation to the student's t multiplier of 3.143 thatis used to determine the MDL. Stdev, refers to the standard deviation ofthe percent recovery.

The BMF prefilter (Comparative Example C-1), an SPE media containingPTFE without the prefilter (Comparative Example C-2), and the one piecearticle of Example 1 were also tested and compared for recovery asoutlined above using the EPA standard hexadecane/stearic acid 50/50solution. The results are tabulated in Table 3.

TABLE 3 Example # of Samples Percent Recovery C-1 2 27.5 C-2 2 72.5Example 1 >10 88-98

Comparative Examples C-3 through C-5

The performance of several commercially available SPE mediums wascompared to the performance of the one-piece article of Example 1 whenexposed to several waste water challenges. Recovery data was determinedusing the “Method of Use of an SPE Disk” procedure described above. Flowrate data was determined by timing the flow of 1 liter samples of thewastewater challenges through the SPE constructions. Tables 4-7summarizes the results.

Referring to Tables 5-7. Example “C-3” is a commercially available SPEmedia that uses a porous glass fiber media to contain the C18 sorbentparticles; Example “C-4” is commercially available SPE media cartridgethat is preassembled in a laminar configuration within a polymerhousing—it contains a glass fiber prefilter over approximately 1000 mgof loose C18 sorbent particles supported on a support material thatprevents the C18 particles from being released; Example “C-5” is acommercially available disk made of borosilicate fibers containing C18sorbent particles sandwiched, but not bonded, between two polypropylenenonwoven support.

“SD” is the standard deviation of recovery data. “P” indicates that thefilter became unplugged during the analysis procedure. The StandardIndustry Classification (SIC) code is an EPA designation describing atype of business activity which generates particular wastewaters. Thesewastewater samples were effluent discharge water. The data is an averageof 5 separate tests for each SIC.

SIC Codes water tested include: 7219—laundry and garment cleaning,4952—sewage systems, 2911—petroleum, 4173—bus maintenance,3499—fabricated metal production, 2024—food manufacturing such as icecream. The recovery upon the typical oil & grease test as outlinedabove.

TABLE 4 Recovery and Flow Properties of Example 1 SIC Flow (min)Recovery (mg) SD 7219 43.00 38.40 5.20 4952 2.80 3.49 1.39 2911 4.00330.88 15.40 4173 8.60 35.11 5.82 3499 26.60 6.78 2.24 2024 9.00 23.031.16

TABLE 5 Recovery and Flow Properties of Comparative Example C-3 SIC Flow(min) Recovery (mg) SD 7219 65.80 27.38 6.85 4952 2.40 6.14 1.26 29112.20 299.88 33.80 4173 33.20 21.27 2.39 3499 6.40 6.02 1.94 2024 2.603.12 1.72

TABLE 6 Recovery and Flow Properties of Comparative Example C-4 SIC Flow(min) Recovery (mg) SD 7219 44.00 34.79 8.42 4952 4.00 0.40 0.12 29116.00 368.21 21.76 4173 5.00 23.40 3.56 3499 19.00 7.38 1.94 2024 65.3018.45 14.40

TABLE 7 Recovery and Flow Properties of Comparative Example C-5 SIC Flow(min) Recovery (mg) SD 7219 P P P 4952 5.20 0.73 0.14 2911 67.80 251.1218.50 4173 5.00 12.86 2.99 3499 74.50 6.19 4.53 2024 P P P

Referring to Tables 4-7, it is apparent that the one-piece multilayerextraction disk format efficiently recovered hydrocarbon extractablesfrom all the SIC wastewater challenges. Furthermore, it was found thatthe one-piece disk did not plug in any challenge. In terms of flowtimes, referring again to Tables 4-7, the one-piece multilayerextraction disk format provided fast flow times, overall.

Example 3 and Comparative Example C-6

A number of melt blown microfiber webs having a range of fiber diametersand solidities were prepared using a polypropylene resin (availableunder the trade designation ESCORENE 3505G, available from EXXON Corp.)substantially as described in Wente, Van A., “Superfine ThermoplasticFibers,” Industrial Engineering Chemistry, vol. 48, pp 1342-1346. Thewebs were collected on a single drum collector set at approximately 25cm from the die tip. Effective fiber diameter as calculated according tothe methods set forth in Davies, C.N., “The Separation of Airborne Dustand Particles” Institution of Mechanical Engineers, London, proceedings1B, 1952. Web thickness measurements were made using a 100 grams per 10square centimeter force on the webs. Solidity of the webs was calculatedfrom weight and thickness measurement of webs using the relationship:solidity equals mass of web divided by polymer density divided by volumeof the web.

Several BMF prefilters (Examples 2-4 in Table 8) of varying physicalproperties were prepared and tested individually without an SPE medium(i.e., solely as a prefilter) for flowtimes using 150 mg/L of SAE finedust. Additionally, a commercially available BMF prefilter (ComparativeExample C-6) was tested. Flow time data indicates the effect thatthickness, basis weight, and solidity have on the prefilters' capacityto maintain rapid flow without plugging. Lower flow times indicatedbetter performance. Based on this data, it was concluded that lowersolidity, higher basis weights and thicker prefilters provided maximumperformance (low flow time).

TABLE 8 Prefilter Performance Thickness Basis Weight Flowtime Product(mm) (g/sq meter) % Solidity (sec) Example 1 3.5 220 5.1 24 PrefilterExample 2 2.3 106.0 4.7 26 Example 3 1.8 173.0 9.6 32 Example 4 1.4 99.06.3 36 C-6 0.3 71.5 19.5 330

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein. The complete disclosures of all patents, patentdocuments, and publications cited herein are incorporated by referenceas if each were individually incorporated by reference.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein. The complete disclosures of all patents, patentdocuments, and publications cited herein are incorporated by referenceas if each were individually incorporated by reference.

What is claimed is:
 1. A one-piece multilayer solid phase extractionarticle comprising a) a first porous support layer, b) a second poroussupport layer attached at least one thermo-mechanical attachment site tosaid first porous layer, and c) a layer of solid phase extraction mediumdisposed between, and in intimate contact with, the first and secondporous support layers such that a portion of the solid phase extractionmedium is bound within the thermo-mechanical attachment site.
 2. Thearticle in claim 1 wherein at least one of said first and second poroussupport layers is a thermoplastic material.
 3. The article in claim 2wherein said thermoplastic material comprises a polymer selected fromthe group consisting of polyolefin, polycarbonate, polyester andpolyamide.
 4. The article in claim 2 wherein said thermoplastic materialcomprises a polyolefin selected from the group consisting ofpolyethylene, polypropylene, ethylene/propylene copolymers and blendsthereof.
 5. The article in claim 1 wherein said thermo-mechanicalattachment site is formed by ultrasonic welding.
 6. The article in claim1 wherein said first porous support layer is a pre-filter having asolidity of no greater than about 20%, a thickness of at least about 0.5mm, and a basis weight of at least about 70 g/m².
 7. The article ofclaim 1 wherein said first porous support layer is a non-woven web. 8.The article of claim 7 wherein said nonwoven web comprises thermoplasticmicrofibers.
 9. The article of claim 8 wherein said microfibers are meltblown.
 10. The article in claim 9 wherein said melt blown microfibershave a diameter of no less than about 0.1 microns and no greater thanabout 20 microns.
 11. The article in claim 1 wherein said first poroussupport layer comprises multiple layers of porous material, wherein atleast one of said multiple layers of porous material is in intimatecontact with said layer of solid phase extraction medium.
 12. Thearticle in claim 1 wherein the second porous support layer comprisesmultiple layers of porous material, wherein at least one of saidmultiple layers of porous material is in intimate contact with the layerof solid phase extraction medium.
 13. The article in claim 1 whereinsaid solid phase extraction medium comprises a fibril matrix comprisingthe fluoropolymer with sorptive particles enmeshed therein.
 14. Thearticle in claim 13 wherein said sorptive particles comprise silicaparticles coated with an aliphatic hydrocarbon.
 15. The article in claim13 wherein said solid phase extraction medium further comprises glassparticles enmeshed within the fibril matrix.
 16. The article in claim 11which is in the form of a circular disk or a polygon.
 17. The article inclaim 16 wherein said thermo-mechanical attachment site is at theperimeter.
 18. The article in claim 16 wherein the solid phaseextraction medium is bound within said thermo-mechanical attachment siteat at least one point within the perimeter.
 19. The article of claim 1wherein said first and second porous support layers comprise the samethermoplastic polymeric material.
 20. The article of claim 1 wherein thesolid phase extraction medium comprises a fluoropolymer.
 21. A method ofextracting an analyte from a sample comprising a) providing a one-piecemultilayer solid phase extraction article comprising i) a first poroussupport layer, ii) a second porous support layer attached to said firstporous support layer at at least one thermo-mechanical attachment site,and iii) a layer of solid phase extraction medium disposed between, andin intimate contact with, the first and second porous support layerssuch that a portion of the solid phase extraction medium is bound withinthe thermo-mechanical attachment site; and b) passing the sample throughsaid one-piece multilayer solid phase extraction article.
 22. The methodaccording to claim 21, wherein said first porous support layer is apre-filter having a solidity of no greater than about 20%, a thicknessof at least about 0.5 mm, and a basis weight of at least about 70 g/m².23. The method according to claim 21 wherein at least one of said firstand second porous support layers comprises a thermoplastic material. 24.A method of thermo-mechanically making a one-piece multilayer extractionarticle comprising: a) stacking a first porous support layer, a secondporous support layer, and a layer of solid phase extraction mediumtherebetween; b) positioning said stack of layers in an ultrasonicwelder, said welder comprising an anvil and an ultrasonic horn; and c)pinching said stack of layers between said anvil and said horn to format least one thermo-mechanical attachment site between said first andsecond porous support layers, wherein at least a portion of the solidphase extraction medium is bound within said thermo-mechanicalattachment site.
 25. The method according to claim 24 wherein said anvilcomprises a cutting angle sufficient to cut said stack of layers atsubstantially the same time as the formation of said thermo-mechanicalattachment site.
 26. The method according to claim 24 wherein at leastone of said first and second porous support layers comprises athermoplastic material.
 27. The method according to claim 26 whereinsaid thermoplastic material comprises a polymer selected from the groupconsisting of polyolefin, polycarbonate, polyester and polyamide. 28.The method according to claim 26 wherein said thermoplastic polymericmaterial comprises a polyolefin selected from the group consisting ofpolyethylene, polypropylene ethylene/propylene copolymers and blendsthereof.
 29. The method according to claim 24 wherein said first poroussupport layer is a pre-filter having a solidity of no greater than about20% a thickness of at least about 0.5 mm and a basis weight of at leastabout 70 g/m².
 30. The method according to claim 24 wherein said firstporous support layer comprises a non-woven web.
 31. The method accordingto claim 30 wherein said nonwoven web comprises micro fibers.
 32. Themethod according to claim 31 wherein said microfibers are melt blown.33. The method according to claim 32 wherein said melt blown microfibershave a diameter of no less than about 0.1 microns and no greater thanabout 20 microns.
 34. The method according to claim 24 wherein saidfirst and second porous support layers comprise the same thermoplasticpolymeric material.
 35. The method according to claim 24 wherein saidsolid phase extraction medium comprises a fibril matrix comprising thefluoropolymer having sorptive particles enmeshed therein.
 36. The methodaccording to claim 35 wherein said sorptive particles comprise silicaparticles coated with an aliphatic hydrocarbon.
 37. The method accordingto claim 35 wherein said solid phase extraction medium further comprisesglass particles enmeshed within the fibril matrix.
 38. The method ofclaim 24 wherein the solid phase extraction medium comprises afluoropolymer.